those Smart Sam tires *are* CX tires.

before you do anything else, try dropping the air pressure in the x38's you have when you hit the trails. if you're around 170 lbs, and the bike riding position is such that you have around 100 lbs on the back wheel and 70 on the front, you could try 60psi rear, 50psi front, and see how that tracks. when you get back to the pavement and want to go fast/far, pump them back up +10 or +20 psi.